Definition: You are given a question on high school biology. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: The Krebs cycle in humans occurs in the
(A)mitochondrial matrix (B)inner mitochondrial membrane (C)outer mitochondrial membrane (D)intermembrane space

A